Visual examination is often performed on used tires prior to the retreading process. The purpose of the visual examination is to identify tires with flaws such as cuts, holes, and nails or the like imbedded therein. It is essential that the visual examination be time efficient, yet reliable. Identified flaws in tires may be repaired prior to the tires being buffed and retreaded.
While visual examination is often reasonably accurate, flaws are frequently missed due to human error or to the absence of visual evidence of the flaws. Undetected flaws may give rise to defective retreads by allowing high pressure air to flow through the flaws and into the tire structure, causing separation of tire components, heat, and generally degradation of the tire. Any of these defects may give rise to the failure of the tire either in the retread shop or during use on the road.
As alternatives to visual examination, one class of machines detects holes in inflated tires immersed in a liquid. Escaping air from these holes may be directly observed in the form of bubbles.
U.S. Pat. Nos. 4,297,876 and 4,327,579 disclose ultrasonic tire testing apparatus for detecting separations and/or holes in vehicle tires. The system disclosed therein employs a through transmission method of ultrasonic inspection. An ultrasonic transmitter array and an ultrasonic receiver array are both mounted in a non-contacting, non-critical relationship with the tire undergoing inspection. The inspection is performed during a single tire revolution. The ultrasonic transmitters are pulsed and the receivers are sampled at predetermined time intervals. The predetermined time intervals are related to the transmitter/receiver/tire geometry. The method and apparatus disclosed eliminate potential problems of talk-around and standing waves. The problem of transmitter-transmitter interference is eliminated by transmitter frequency separation and transmitter array pointing geometry. The problem wherein tread pattern fluctuations in the received signal interfere with flaw detection is eliminated by the use of a finite sample data filter with a period adjusted to the period of the tread pattern.
U.S. Pat. No. 4,520,307, hereby incorporated by reference, discloses a high voltage tire testing apparatus for detecting nails, cuts and/or holes in vehicle tires. The apparatus employs a high voltage head mounted within the tire and a reference head disposed outside the tire opposite the high voltage head. The high voltage head and reference head span the tire tread axially. The inspection may be performed in one tire revolution with high voltage pulses that are impressed upon the high voltage head. The amplitude and pulse widths of the high voltage pulses are variably selected to be commensurate with the type of tire being examined. When a nail, cut, or hole in the tire passes between the high voltage head and the reference head, an electric arc forms and current passes through the tire. The arc may be visually observed or electronically detected via an electronic detection circuit in which a lamp lights and the tire rotation is stopped when a flaw is encountered. The flaw may then be located manually.
U.S. Pat. No. 6,304,090, hereby incorporated by reference, also discloses a high voltage tire testing apparatus. The apparatus disclosed therein detects tire flaws using tire spreaders and rotating apparatus that are generally already present in a facility for retreading tires. In one embodiment, the high voltage tire testing apparatus includes a frame that is sized to fit in the interior of the tire. The frame includes a probe or pin and front and rear frame wheels. The probe or pin is electrically connected to a high voltage source to create a high voltage field near the inner surface of the tire. If the tire testing apparatus is operated on a tire rotation stand with rollers, the rollers are in electrical contact with the voltage source and, for example, grounded. Operationally, the frame is inserted into the interior of a tire to be examined for flaws and the tire is rotated. During rotation, the frame wheels maintain the tester frame, and hence the probe, near or at the bottom of the tire. Upon encountering a flaw in the tire, an electric arc is generated through the flaw between the probe and the grounded roller. The person conducting the examination sees and hears the arc and thereby detects the tire flaw. However, in noisy facilities, seeing and/or hearing the arc becomes more difficult. Therefore, tire flaws “detected” by this apparatus may not be observed by the person conducting the examination and tires with unrepaired flaws may be recapped. These flawed recapped tires pose dangers to users and sources of liability to persons recapping tires. Therefore, a flaw detection apparatus is needed that provides an indication of a tire flaw in addition to the observation of a generated electrical arc.